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West Country Conversion to P4 part 3 - rolling chassis


ullypug

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A couple of successful evening sessions has seen the rods made up and fitted. The upper keeper plate was fitted and happily the chassis ran up and down on the test track under finger pressure and when relatively slightly sloped. Huge sigh of relief as always!

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I've also fitted 60 thou black plasticard overlays to the chassis block. Some bits have yet to be hacked off (rear pony) and won't be until the last moment so I don't take too much off.

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We're now in the realms of having to choose the prototype so this one will be Watersmeet 34030 as it was a long term Exmouth Junction resident. There were so many variances between the different engines and one of them is the knuckle position in the rods. This one will be behind the con rod which (if I've understood it right) matches the 21C101-31 engines. Others were forward, until some of them were modified.

 

The front rod is only a single thickness on the crankpin to allow for the crankpin nut to be clear the con rod/slide bar.

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The Irwell Press book really is a must if you're contemplating doing one of these. It also gives a couple of very useful front end shots of the bogie. I decided I needed to do something about where I'd got to so far and added some detail from plasticard and 8BA brass studding. This configuration was one of a later series of modifications, meaning Watersmeet is going to be a 1962 condition with the cut down tender. The original raves were not cut down until 1960 according to the Irwell book.

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Next it's the cylinders and con rods. I'm going to use the Hornby con rod. Gibson bushes have been fitted. I've found some brass tube and will see if I need to sleeve the piston rod.

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The front of the bogie is very neat.

I fudged mine and hid it all under black paint.

The single thickness front rod is an interesting idea. It is tight there even in EM.

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If you turned the crankpin nut the other way round (i.e. with the small diameter "cap" to the inside), this may be a way of saving a little space. Ultrascale makes a recessed crankpin which works in a similar way so that you can still use a near full-thickness coupling rod in front.

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Thanks for the comments guys.

I've used the 'half rod' approach on all the P4 locos I've built. I think I first saw it used by John Brighton. The crankpin nut will be thinned down with a carborundum disc once I've added thread locker. In my experience as long as you've 2 active threads in the nut it all holds together. You're right in that you can turn it round (at the expense of having a larger hole through the rod) if you need more space. I'll see how things go.

Then there's also the option of moving the slide bars out 0.5mm either side (hence the previous sleeved piston rod ponderings) but that really is cheating!

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Now that is very strange I have just started a kit to build a west country with a cut down tender, I have to sort the cab to get an 8' 6" one. But I narrowed mine down to 2 prototypes, Watersmeet or Combe Martin. I am more or less decided on Watersmeet as I like the place and go there at every opportunaty.

 

You loco is coming on nicely, the chassis overlays improve no end.

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